Numerous apparatus have previously been developed for the transdermal delivery of drugs and other medicinal compounds utilizing microneedle assemblies. Microneedles have the advantage of causing less pain to the patient as compared to larger conventional needles. In addition, conventional subcutaneous (often intra-muscular) delivery of drugs via a needle acts to deliver large amounts of a drug at one time, thereby often creating a spike in the bioavailability of the drug. For drugs with certain metabolic profiles this is not a significant problem. However, many drugs benefit from having a steady state concentration in the patient's blood stream; a well-known example of such a drug is insulin. Transdermal drug delivery apparatus are technically capable of slowly administering drugs at a constant rate over an extended period of time. Alternatively, transdermal drug delivery apparatus may administer drugs at variable rates. Thus, transdermal drug delivery apparatus offer several advantages relative to conventional subcutaneous drug delivery methods.
There is a desire for at least a portion of a transdermal drug delivery apparatus that provide a new balance of properties.